Media Isolated Pressure Sensor With Bonded Wafer Cavity
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Solution Overview
Problem
Existing pressure sensors face challenges in high-pressure applications due to potential damage from corrosive or conductive media, which can cause electrical shorts and failure of the die attach, especially when exposed to downward pressure.
Innovation Solution
A media isolated pressure sensor design featuring a bonded wafer substrate with a buried sealed cavity and a top cap that isolates bond pads from the media, allowing pressure to be applied to the sensing diaphragm while preventing electrical component damage, using a bonded silicon wafer with a sensing diaphragm and piezoresistive sense elements connected via bond pads, and a top cap that secures the pressure sensing element to a carrier, preventing dislodgement.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pressure sensor allows fluid pressure to be applied to the top side of the pressure sense die, then pressure sensing is enabled, but corrosive or conductive media can cause damage to components and electrical shorts
Solution Approach 1:
The pressure sensor is divided into distinct functional zones: a media-exposed sensing area and a protected electrical component area. The sense die includes a diaphragm portion that contacts media and a separate region housing bond pads and electrical components, physically segregated to prevent media damage while maintaining pressure sensing functionality.
Solution Approach 2:
The diaphragm acts as an intermediary element that transmits mechanical stress from media contact to the sense elements without requiring direct exposure of electrical components. The diaphragm converts media pressure into mechanical stress that is then detected by protected piezoresistive elements, isolating the electrical circuitry from harmful media exposure.
2Stress or pressure
If high pressure is applied to the backside of the sensor, then pressure measurement capability is improved, but the die attach may fail due to excessive downward pressure
Solution Approach 1:
The sense die is positioned and configured to counterbalance the downward pressure force generated by high pressure application. The mechanical design distributes the pressure load through the diaphragm structure in a manner that prevents excessive force from concentrating on the die attach interface, thereby preventing attachment failure while maintaining high pressure measurement capability.
3Adaptability or versatility
If the pressure sense die is mounted to allow media contact with electrical components, then device complexity is reduced, but the sensor cannot be used in corrosive or conductive environments
Solution Approach 1:
The sensing function and isolation function are merged into a single integrated diaphragm structure. The diaphragm simultaneously serves as the media interface, the stress transmission element, and the protective barrier for electrical components. This integration achieves media isolation without requiring separate complex isolation mechanisms, enabling use in corrosive environments while maintaining reasonable device simplicity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a robust pressure sensor capable of withstanding high pressures by isolating sensitive components from corrosive or conductive media, reducing the risk of electrical shorts and enhancing long-term performance and reliability.
Implementation Method 1
The pressure sense die is often configured to detect a pressure of a sensed media by converting mechanical stress induced by the sensed media in a sense diaphragm of the pressure sense die into an electrical output signal
Data Source
AI summary
A pressure sensor includes a pressure sensing element and a top cap. The pressure sensing element includes a bonded wafer substrate having a buried sealed cavity. A wall of the buried sealed cavity forms a sensing diaphragm. One or more sense elements may be supported by the sensing diaphragm and one or more bond pads are supported by the upper side of the bonded wafer substrate. Each of the bond pads may be positioned adjacent to the sensing diaphragm and electrically connected to one or more of the sense elements. The top cap may be secured to the upper side of the bonded wafer substrate such that an aperture in the top cap facilitates passage of a media in a downward direction to the sensing diaphragm. The top cap may be configured to isolate the bond pads from the media.